The invention relates to an ignition coil for internal combustion engines.
In the case of ignition coils, a high voltage of up to 50 kV must be produced in a very limited space.
In order to obtain a long useful life, the coil must be insulated as well as possible, a construction not producing partial discharges being ideal. Because of the electrical insulation, a coil with low partial discharges is very bulky. The magnetic leakage fields are large with conventional solutions, and the magnetic coupling between the primary and secondary coil is poor.
The object of the invention is to provide a coil improved with respect to useful life and to a compact construction.
According to the invention, this is obtained by means of an ignition coil for internal combustion engines that is characterised by two or more transformer stages connected in a cascade arrangement one behind another, wherein the secondary windings of all the transformer stages are connected in series onto a spark plug.
With such a construction, the individual transformer stages can be constructed more compactly, as the high voltage required is produced in several stages, wherein the individual stages can easily be insulated one from another. In the respective stages themselves, the voltages are lower with respect to one another, whereby the gaps between the windings can be minimised. As a result, a better magnetic coupling is obtained. Leakage fields can be reduced. With this multiple stage construction, the required insulation gaps are smaller, which allows a closed iron core, or respectively a general ferromagnetic core, to be used in each individual transformer stage, while at the same time preserving a relatively compact construction. In this way the magnetic flux can be better controlled.
In addition to a more compact construction, the ignition coil according to the invention is also characterised by a longer useful life, in particular as, due to lower voltages, it is easier to prevent partial discharges via the insulator.
Furthermore, the cascade arrangement allows a large degree of freedom in the sizing of the ignition coil, both from the electrical point of view and from the point of view of the mechanical construction. It is thus possible, for example, to arrange the individual transformer stages geometrically in almost any arrangement with respect to one another. An arrangement in which the individual transformer stages are xe2x80x9cthreadedxe2x80x9d one behind another on a common imaginary axis is advantageous. There are, however, other possibilities for arrangement. From the electrical point of view, an adaptation to the prevailing conditions can be made, for example, by different transformation ratios in the individual transformer stages. It is also possible to size the input side transformer stages with respect to the volume of the core and the wire thickness of the windings smaller than the output side stages, which allows a more compact and slimmer mode of construction in the output area.
It is also possible to feed the primary winding of the transformer stages using separate voltage sources, for example, by means of a capacitor circuit or a high-frequency ignition circuit. Essentially, the ignition coil according to the invention is suitable in the most different of configurations, both for capacitor ignition circuits and for high-frequency ignition circuits, wherein there is particular suitability for high-frequency ignition circuits, which can transmit frequencies up to the 100 kHz range. Further advantages and details of the invention will be explained with reference to the following description of the drawings.